Apparatus for mixing working gas and additional gas in arc plasma torches with a very high emission velocity of the plasma stream



L. HAASE ET AL 3,489,876 OR MIXING WORKING GAS AND ADDITIONAL GAS IN SMA TORCHES WITH A VERY HIGH EMISSION VELOCITY OF THE PLASMA STREAM Jan. 13, 1970 APPARATUS F ARC PLA Filed Dec. 15, 1966 INVENTORS LOTHAR HAASE BY RUDOLF POCHERT J W y ATTORNEY.

APPARATUS FOR MIXING WORKING GAS AND US. Cl. 21975- 2 Claims ABSTRACT OF THE DISCLOSURE An apparatus for mixing the working gas and additional gas in arc plasn'la torches with high emission velocity of the plasma stream into a gas discharge chamber, comprising a main housing, two longitudinal hd'psing members in the main housing, a gas connection connected to each of the housing members, first and second valve tappets received in each of the housing members, respectively, and a first and second magnet valve disposed in each of the housing members, respectively, cooperating with the first and second valve tappet, respectively, and having a first and second orifice, respectively," leading into a. first and second lower chamber, respectively. A nozzle is provided in one of the lower chambers communicating therewith, and forms an annular slot about its outer periphery, the other of the lower chambers communicating through the annular slot. A cathode is fixed at one end of the main housing, the lower portion ofthe cathode being surrounded by gases fed from at least one of the lower chambers, and a cutting nozzle is; disposed at .the lower end of the main housing and cooperates with the lower portion of the cathode. i

The present invention relates to an apparatus for mixing the working gas and additional gas in arc plasma torches with a very high emission velocity of the plasma stream.

Arc plasma torches are known and operate in accord ance with the principle of an ionized gas arc, with which high temperatures for the working of working material, mostly for fusion cutting of work pieces; are obtained.

In its simplest case and preferably in small outputs, only one gas, the so-called working gas, which comprises, for instance, argon or nitrogen, is used. This method of operation has a low efiiciency and is, in addition, applicable only up to a low electrical output, since these gases maintain the electrical resistance of the are low and poorly convey the heat. In case of higher electrical outputs, the gas is heated so much in the gas discharge chamber, that the outer cooling gas jacket, which is supposed to protect the cutting nozzle, is penetrated and arcingover occurs between the cutting nozzle and the work piece.

In order to make possible an operation with high electrical outputs, an additional gas is applied to the arc, in addition to the working gas, for instance, hydrogen and in particular only upon starting the main arc, which increases the electrical resistance of the arc and conveys the heat better.

The timing of the appearance of this additional gas in the gas discharge chamber is very important for the safe operation of the plasma burner, for which reason advantageously magnet valves are applied for the control of the additional gas, which magnet valves are arranged as close as possible to the gas discharge chamber. If this timing is too soon, the pilot are required for the starting 3,489,875 Patented Jan. 13, 1970 of the main arc and ignited before with the working gas, is extinguished. If the timing is too late, one obtains at first the operation without additional gas, whereby the cutting nozzle is damaged or destroyed by overarcing.

By the additional gas, in addition to the increase of the upper output limit, the efficiency is improved by exploitation of the recombination heat and the output density is increased in the plasma ray. By reducing the diameter of the bore of the cutting nozzle, one obtains an additional increase of the output density and of the exit velocity of the plasma ray.

Plasma burners with very high exit velocity of the plasma ray require, as it is known, a high operational pressure of the operation gases, in order to obtain the gas quantity required for the transportation of a large energy. Since the plasma operates in the direction of narrowing the nozzle, different gas-through puts are obtained in case of different electrical outputs, which gas through-puts contrary'to the desired through-put of the gas, are in reversed order proportional to the output. Furthermore, during ignition of theplasma, the pressure in the discharge chamber increases. This leads to the drawback that also the mixing ratio, in particular in case of gases with very different specific weights, is changed so much, that the operation cannot be maintained.

It is one object of the present invention to provide an apparatus for mixing of the working gas and of the additional gas in arc plasma burners with very high exit velocity of the plasma stream, wherein, while avoiding the drawbacks of the known devices, a constant mixing ratio is obtained and which obtains also an extremely constant gas throughput during the entire duration of operation, also upon changing the electrical output.

It is another object of the present invention to provide an apparatus for mixing working gas with additional gas in arc plasma torches with a very high emission velocity of the plasma stream, wherein the negative influences of the nozzle narrowing and of the pressure increase is avoided.

It is still another object of the present invention to provide an apparatus which mixes the working gas and additional gas in arc plasma burners, wherein, for the purpose of obtaining a nearly constant mixing ratio and a small change of the gas throughput upon change of the electrical output, a pressure drop introduced prior to the gas discharge chamber. of the plasma burner, which is brought about by the insertion of pressure orifices. By the use of a known injector mixing nozzle, the pressure orifices are disposed advantageously between the mixing nozzle and the magnet valves for all working gas an the additional gas.

The technically economical effects, particularly the technical progress of the present invention resides in the fact that, by the appreciably higher pressure in front of the pressure orifices than the pressure in the gas discharge chamber, the mixing ratio remains nearly constant by the pressure variation in the gas discharge chamber caused by a change of the electrical output, while the gas throughput sets itself in accordance with the difference between the pressures in front and behind the pressure orifices.

With these and other objects in view which will become apparent in the following detailed description, the present invention will be clearly undersfood in connection with the accompanying drawing, in which: the only figure discloses an axial section through a plasma torch.

Referring now to the drawir g, the apparatus comprises connections 8 and 9 for the working gas and the additional gas, respectively, which gases are operational gases available at high pressure. A magnet valve 4 is'disclosed in open position and a magnet valve 5 is shown in closed position. In the open position of the magnet valves 4 and 5, the working gases flow through bores 21 and 22 of the valve tappet 23, and through the pressure orifice 1, the additional gas through the bores 24 and 25 of the valve tappet 26 and through the pressure orifice 2 to the mixing nozzle 3. The pressure orifices 1 and 2 are inserted in the housing 19 and 20 of the magnet valves 4.; and The mixing nozzle 3 comprises two concentrically disposed nozzles 15 and 16. The outer nozzle 16 forms an annular slot about the inner nozzle 15. The working gas flows through the nozzle 15 and sucks thereby the specific lighter additional gas through the nozzle 16 from the gas conduit 17 in the mixing bore or conduit 18 where both gases admix. The gas mixture surrounds the cathode carrier l1 and enters into the gas discharge chamber 6 and emerges from the cutting nozzle 7. The cathode is, as it is known, clamped in the cathode carrier 11, which is insulated by the insulator 12 relative to the main housing 13. A pilot are burning between the cathode 10 and the cutting nozzle '7, which pilot is driven out from the cutting nozzle 7 by the carrier gases heated by the pilot arc in the gas discharge chamber, operates as a narrowing of the cutting nozzle 7, whereby the pressure in the gas discharge chamber increases. To a still higher degree as is thus the case, if the main arc, which burns between the cathode 10 and the work piece, 14, is in operation.

Variations of the electrical output of the main arc cause accordingly likewise pressure variations in the gas discharge chamber 6.

By means of the pressure orifices 1 and 2, the gas pressures in front of the pressure orifices 1 and 2 are still appreciably higher than the pressures in the gas discharge chamber 6. For this reason, pressure variations in the gas discharge chamber affect only slightly the gas throughput, which adjusts itself correspondingly to the pressures prevailing in front of and behind the pressure orifices 1 and 2. The mixing ratio between working gas and additional gas remains thus approximately constant. The pressures in front of the orifices 1 and 2 are chosen advantageously so high, for instance atmospheres above atmospheric pressure, such that there occurs on the one hand, a least possible variation of the gas throughput and a perfect ignition and operation of the plasma burner, and, on the other hand, also still an economical exploitation of the gas bottles of the carrier gases is obtained. The diameter of the pressure orifices 1 and 2 follows in accordance with the desired mixing ratio and the specific weight of the carrier gases, whereby the pressures in front of the pressure orifices 1 and 2 are equal as much as possible for both carrier gases. The adjusted gas pressures do not need any change or variation, even upon application of nozzles 7 with different diameters, since the mixing ratio and the gas throughout are determined by the pressure orifices 1 and 2.

The present invention consists not only merely in the execution of a pressure drop, but in the arrangement and application, respectively, of this pressure drop in plasma burners. As known, the pressure rises during the ignition of the pilot arc in the gas discharge chamber and likewise the composition of the gas mixture which arrives for the discharge changes, By the discharge chamber is understood the space between the nozzle and the cathode. The discharge burns mainly in the cone 6. It is also in certain measure in the cylindrical part about the cathode carrier and spreads out in a direction towards the mixing nozzle 3. The known plasma burners and generally also welding burners with mixed working gases work with the principle of the injector mixing nozzle. In order now to assure a stable operation with variable output and a perfect ignition also upon insertion over the work piece, an adjustable pressure drop is produced over pressure step orifices in front of the mixing nozzle, as well as in th o dui of th add t on l gas a d l o i t e o g gas conduit. On the basis of this pressure drop, the unique adjustable mixing ratio of both gases remains constant independent of the pressureand output-ratio in the discharge chamber. This constant ratio is obtained by the arrangement of the pressure orifices and the mixing noz- Zle.

While we have disclosed one embodiment of the present invention, it is to be understood that this embodiment is given by example only and not in a limiting sense, the scope of the present invention being determined by the objects and the claims.

We claim:

1. An apparatus for mixing the working gas and additional gas in arc plasma torches with high emission ve locity of the plasma stream into a gas discharge chamber, comprising a main housing,

two longitudinal housing members received in said main housing,

a gas connection connected to each of said housing members,

a first and second valve tappet received in each of said housing members, respectively,

a first and second lower chamber in said housing members, respectively,

a first and second magnet valve disposed in each of said housing members, respectively, to cooperate with said first and second valve tappet, respectively,

a first and second orifice, respectively, leading into said first and second lower chamber, respectively,

said first and second magnet valve cooperating with saidfirst and second orifice, respectively, to pass gases through said first and second orifice,

a nozzle in one of said lower chambers communicating therewith,

said nozzle defining an annular slot about its outer periphery,

said other of said lower chambers communicating through said annular slot,

a cathode fixed at one end of said main housing,

a cathode holder received in said main housing and retaining said cathode in a predetermined position, the lower portion of said cathode being surrounded by gases fed from said one of said lower chambers, and

a cutting nozzle disposed at the lower end of said main housing and cooperating with said lower portion of said cathode.

2. The apparatus, as set forth in claim 1, which includes a mixing conduit spaced about said outer periphery of said nozzle forming said annular slot,

said first and second orifice disposed between said mixing conduit and said first and second magnet valve, respectively,

said nozzle communicating said one of said lower chambers with said mixing conduit} said annular slot communicating said other of said lower chambers with said mixing conduit, and

said mixing conduit communicating with said lower portion of said cathode for feeding gases thereto.

References Cited UNITED STATES PATENTS 2,960,594 11/1960 Thorpe 210-45 3,089,944 5/1963 Mathews 2l9-74 JOSEPH V. TRUHE, Primary Examiner I. G. SMITH, Assistant Examiner U-S: 1- X-R: 19- 1 

